Glow discharge lamp



March 14, 1939. C)I C; BLE|CHER 2,150,356

GLOW DISCHARG LAMP I Filed July 21, 195e HMVHHHHA /NVE/VTR O. C. BLE/CHER By ma@ Patented Mar, 14, i939 PATENT OFFICE GLOW DISCHARGE LAMP otto c. leicner, Brooklyn, N. Y., assigner to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application July 21, 1936,' Serial No. 91,642

'z-olaims. (ci. 17e- 122) UNITED. sita'lris4 This invention relates to glow discharge devices .and more particularly to positive column lamps;

United States Patent 1,912,146, issued May 30,

' 1933, to J. B. Johnsonwdiscloses a positive column glow lamp vcomprising an enclosing vessel charged with a mixture of a monatomic and a diatomic gas and including a cylindrical cathode, a glass support which surrounds the cath inV ode, engages its outer surface and extends be-' yond it, the extension'being provided with a capillary opening, and` an apertured anode. The cathode, capillary opening andv aperture in the anode are axiallyy aligned, and the discharge,

which occurs. between the inner surface of the cathode and the walls' of the anode aperture,

passes throughand is concentrated in'the capillary opening to provide an intense spot of light which may beusefully employed in signalingsystems, for example, in sound recording, picturel transmission and television systems.

f An object of this invention is to provide a lamp of the type described above` having improved .operating characteristics.`v

Another object is to provide a glow discharge lamp in which the breakdown and extinction voltages are substantially alike.k

A feature of theinvention relates to the use of a metallic member having a taperedy capillary opening through which the discharge passes.1

, Another featurerelates to the use of the metallic member, as an auxiliaryanode to effect breakdown of the discharge path. Y

In accordance with one embodiment of the invention, vthe discharge device comprises a transparent vesselwhich encloses a cylindrical cathode, extending axially of the vessel, and an apertured anode,l a metallic member intermediate the cathode and anode, and containsa gaseous atmosphere, such as a monatomic gas.. The metallic i member comprises ,a cylindrical portion surrounding the cathode, and a portion which tapers ina direction toward the anode and is provided with aitapered capillary opening. The cylindrical cathode-.capillary opening and anode aperbut for starting purposes, i. e., to effect initialionization of the gas charge, this member may be temporarily connected to the anode to provide,

in effect, an auxiliary anode adapted to cooperate with the cathode to constitute a path over which an initial discharge readily takes place. 5 Once this auxiliary discharge is started, the main discharge path is readily bridgd by the normal operating voltage impressed between the main` electrodes.

A description of the invention follows and is v1li illustrated in the attached drawing, in which Fig. 1f is a sectional view taken axially of a. lamp embodying the invention; and

Fig. 2 is a plane view of the lamp shown in Fig. l.

One disadvantage of glow lamps of the type to be hereinafter described, which have been disclosed in the prior art, is that they operate to produce oscillations in the discharge path, when the electrodes are supplied with varying poten- 20 tials. The oscillations are ofla frequency which is independent of the rate of variation of the applied potential, and appear to be caused by an after-ionization or after-glow, resulting from the fact that the walls of the capillary opening 25 becomes negatively charged and acts as a third electrode to cause ionization aftery each cycle. of change in the applied potentials. While the amplitude of the oscillations could be decreased by varying the -pressure of the gas charge and could 3o be completely eliminated by this expedient when varying direct current potentialswere supplied to its electrodes, it was found impossible to eliminate them when the lamp was suppliedwith potential variationshaving diierent frequencies. 35 Again, when alternating current potentials were applied to the electrodes of a lamp of the earlier type and thefrequency of the potential was increased, a loop appeared in its voltage-current characteristic curve. I 40 Electro-optical systems, such as for example, picture, television and sound recording an'd reproducing systems involve the use of signal potentials which include variations extending over a wide frequency band. In certain cases this 45 bandmay extend from substantially zero frequency to an upper hunting frequency of several thousand cycles or even a million or more cycles for high qualitytelevision operation, and it has been proposed to apply such signal potentials to a glow discharge lamp to control thev production.l of a record or an image of a remote field. It has also been proposed to apply a potential varying. at a carrier` frequency rate to lamps of this type for the purpose of producing nate or scan a picture, a photographic record or an image eld. For distortionless operation it is essential that the intensity'of the light supplied by the lamp faithfully follow the amplitude variations ofthe applied signals or carrier variations.

The amount of distortion resulting from the operation of lamps of the type disclosed in the prior art including'that in the above-mentioned patent to Johnson is well within permissible limits under certain given operating conditions and hence they may be satisfactorily used for many purposes.V However, the present invention provides a construction which possesses many ad-v vantages over those earlier disclosures, chief of which is, that it can be supplied with energiz'` ing potentials of varying frequencies without causing the production of oscillations or a loop in its voltage-current characteristic curve, due to frequency changes.

Referring to the drawing, there is shown a lamp comprising a bulb I,having. a reentrant stem `2 and enclosing a cylindrical cathode 3, a discshaped anode 4, provided with an aperture 5, and a member 6 having 'a cylindrical portion 1, concentric with the cathode, and a cone-shaped extension 8, having a capillary opening 8.

The bulb contains a charge consisting of monatomic gas or'a mixture of monatomic gases. If desirable, the charge-mayinclude, in addition to the monatomic gas or gases, a small quantity of .diatomic gas, the amount being ofthe order given in and for the purpose disclosed in United States Patent 1,871,266, issued August 9, 1932, to F. Gray.

Encircling the stem 2 is a band 9 provided with rods Ill and II for supporting the member 6 and the anode 4. These elements are mounted with the opening in the cathode, capillary opening in the extension 8 and the aperture 5 in the anode axially aligned, and the anode is Supported from the member 6 by short rods I 2 each including 'an insulating bead I3, whereby the member 6 is insulated from the anode 4.

'The reentrant `stern terminates in a press I4 through which a leading-in wire I5 passes to the cathode 3. A leading-in wire I 6 passes through the wall of the stem 2 and extends t the anode 4. This leading-in wire is surrounded by an insulating sleeve I'I, to prevent discharges between it and the cathode. a

The lamp is provided with a base I8, having a pair of contacts I9, respectively connected to the leading wires I5 and I6, and a switch. The electrodes of the lamp are adapted to be connected to an energizing source via the contacts I9, and the switch is'provided to permit a conductor 2|, extending to the member 6, to be connected to the lead-in wire I6, whereby the anode potential may be simultaneously applied to this member and the anode. The lead-in wire 2| is also surrounded by an insulating sleeve 22, to prevent the occurrence of discharges between it and the cathode 3. Under conditions to be hereinafter described, member 6 may be used as an auxiliary anode which cooperates with the cathode to constitute a relatively short path over which a discharge may 'be initiated for starting the lamp.

The switch comprises a pair of co tacts 23 and 24, respectively connected to the lea -in wire I6 and the conductor` 2 I and contact 24 is adapted to be moved into engagement with contact 23 by a pushbutton 25, which extends through the side wall of the base and is held in'the position shown by a spring 26, whereby the switch contacts are carrier modulated light which is used to illumi- -normally disengaged, the conductor wire 2l is disconnected from the ,supply source and, as a result, the member 6 is not supplied with energizing potential.

When it is desired to initiate a discharge within .the lamp, push-button 25 is actuated to connect and is concentrated to produce a small spot of light of extremelyv high brilliance as viewed through the aperture 5. 'I'his light spot can be directly used to scan a picture, sound track, re-

cording surface or nlm or may be used with an optical system for illuminating or scanning an object or eld of view.

The cylindrical portion of the member 6 has a diameter many times that of the larger end of the fcapillary opening, and its length should preferably be-approximately one and a half times the length of the conical section including the capillary. The member, therefore,l constitutes an element having a large superficial area compared with that of the capillary opening, and since it is made of metal, the charge imparted to the walls of the capillary by the passage of the luminous discharge will continuously leak along the surface of the member and thereby cause the latter to become substantially uniformly charged at a potential which does not materially differ from that of the cathode. Consequently, under normal operating conditions, this member Will not act as an auxiliary electrode to produce after-ionization or afterglow and hence will not-cause oscillations to be set up in the discharge path.

For satisfactory use in electro-optical systems, the electrical requirements of a discharge lamp are that the exposure versus current relation 4should preferably be linear, the light of the dis- I contrast, the breakdown voltage and extinction voltage lshould be low and the difference between these two voltages should be as small as possible,

the frequency characteristic should be good, the

lamp should have a long useful life, and it should be reproducible. While these desirable characteristics are partially contradictory, a satisfactory compromise between the conflicting requirements was attained by providing a lamp including an assembly comprising a disc-shaped anode having a rectangular aperture, a glow discharge concentrating member having a cone-shaped portion, provided with a taperedcapillary opening, integral with a cylindrical portion which completely surrounds a tubular cathode. In a typical design of lamp, which has been successfully operated, the anode, concentrating member, and cathode, were of nickel, and the aperture in theanode, the capillary opening and the cathode were axially aligned, and the enclosing bulb contained a charge of pure helium or pure neon. One surface of the anode was separated from the apex of the cone-shaped portion of the concentrating member by a thin was slightly larger than that in the, anode and somewhat smaller than the diameter of that in the apex of the cone-'shaped element. n

'I'he cathode was a thin walled tube and had an internal diameter-of approximately'eight millimeters. The internal diameter ofthe cylindrical portion of the concentrating member was sub-l stantially twice that of the cathode, and it terminated in a plane more remote from the base of the cone-shaped portion than that occupied by the corresponding terminal of the tubular cathode. Thus the cylindrical portion of the concentrating member is spaced apart from andis concentric `with the cathode, and'its length is such as to preclude the possibility `of a discharge occurring between the cathode and the anodel over a'path extending along the outer surface of the concentrating member and around its base; In other words, it insures that the discharge between the electrodes will pass through the capillary opening, which tapers from a diameter of five millimeters at the base of the cone, i. e., adjacent the near end of the cathode, to a diameter of 1.5 millimeters at its apex, or adjacent the anode. r

The use of the metallic member having a capillary opening, in place of a concentrating element of insulating material provided with a capillary opening, resulted in the provision `of a positive column lamp which can be supplied with energizing potentials extending over a wide frequency range without causing free oscillations to be pronated from a tungsten' lamp, activated by the light radiated from the glow=discharge produced in helium. The resiilts serve to illustrate the fact that for current variations of the order commonly used in picture and sound recording systems, the lightintensity may be controlled to provide wide variations in contrast.

Again, lamps of the type described above were supplied with energy from a direct current source and their voltage-current k"characteristics were measured. Certain of 'the lamps contained a gas charge of lpure helium, while the gas charge in others was pure neon. In general they were so designed that a glow discharge was initiated by lapplying a direct current potential of approximately 350 volts across the cathode and anode. When the push button switch was operated to connect the concentrating member to the anode, a discharge was initiated by the application of a potential of about 200 volts. As the voltage-was increased the current fiow in the discharge column increased substantially linearly and the glow discharge, in the helium lamps being tested, was interrupted when the applied voltage was reduced to approximately 225 volts and, in the neon lamps under test, the glow discharge was interrupted when the applied voltage was reduced to about 230 volts. In other words, the breakdown voltage v was reduced from 350 volts to approximately 200 duced in the discharge path, i. e., the presenceof themetal capillary member results 1n stabilizing the frequency characteristic of the lamp. Again its use resulted in a better compromise as to brightness, current range, operating voltage and extinction and breakdown voltages. An important advantage of the use of a tapered capillaryresides in the fact that the voltage required to initiate a discharge vwithin the lamp is far below that required to effect this result in lamps,

' I identical as to design and operating conditions,

u similar to that but which are provided with a straight-walled capillary of the same diameter, i. e., the breakdown voltage of the ,lamp is materially reduced.

` While the brightness of the illumination, supplied by lamps of the type described herein, for

a given value of current in the discharge path between the electrodes, can be varied 'by changing the pressure of the rare gas, this change affects the extinction current, as well as the breakdown, operating and extinction voltages. It was found by experiment that the best compromise with a lamp of given design is obtained by using a charge of helium at approximately seven millimeters of mercury in a lamp for recording purposes, and a charge of neon at approximately.

nine millimeters of .mercury in a lamp which is used to illuminate a record or picture.

Theoperating characteristics of positive co1- umn glow discharge lamps of the type described above was investigated by applying to its electrodes a direct current potential of sufdcient value tol maintain a discharge within the lamp and by varying the current in steps between one mil andy sixty mils. The intensity of the light supplied by the lamp was found to vary substantially linearly y from-a minimum value to a value approximately 170 times that of the minimum value. 4These comparative values were obtained by measuring the direct current output of a potassium-hydride photoelectric cell, the response curve of which is of process nlm when'it is illumivolts, and the extinction voltage of the respective lamps was 225 and 230 volts. When a current of constant amplitude but which varied in frequency from approximately zero frequency to a frequency of several thousand cycles wa's supplied to the lamp, the intensity of the light supplied bythe glowing column was found to be independent of frequency, and an oscillograph study ofthe operation of the lamp failed to indicate the presence of oscillations inthe discharge path.

Life testswere made with a vseries of lamps supplied with current of 20 mils and light current and voltage-current measurements were made at stated intervals. These tests were made under identical operating conditions and indicate that the variation of light with increase in life is small, and at the end of .-1500 hours, the

'in the manufacture of these parts assures the production of lamps having substantially identical operating characteristics, optical properties and useful life. Consequently, lamps of the type herein disclosed, and having these desirable characteristics, are readily reproducible. l

Whilev certain specific details and dimensions have been set forth above, it is to be understood that the important features of the present invention are the use of a metallic member for concentrating the positive column glow discharge and that a, tapering passage terminating in a capillary opening be used to effect the concentration. As to the details and dimensions of the parts, as well as the gas pressure to be used, this will depend largely upon the operating conditions in any given case and the result to-be accomplished.

What isV claimed is:

1. A positive column glow discharge lamp comprising cold electrodes, and, intermediate said electrodes, a-metallic member having a tapered passage terminating in a capillary opening.

2. A positive column glow discharge lamp comf prising a Vcold cathode, a cold anode, and, intermediate said cathode and anode, a metallic member comprising a section surroundlngbut spaced from the cathode and having a conical extension provi-ded with a tapered opening between said section and said anode.

3. A positive column glow discharge lamp comprising a vessel containing gas and enclosing electrodes in the form of a cold anode and a cold cathode, and a hollow metallic member in part surrounding said cathode, the interior wall of said part being cylindrical and symmetrically spaced from the exterior surface of said cathode with respect to the axis of said cylindrical wall, said member being eectively extended into the space between said cathode and anode and having its interior wall in this portion shaped to form a conical channel coaxial with said cylindrical wall with its larger end toward said cathode and its smaller end terminating in a capillary opening. l

4. A positive column glow discharge lamp comprising a vessel containing gas and enclosing electrodes in the form of a cold anode and a cold cathode, a hollow metallic member in part surroundingV said cathode, the interior wall of said part being cylindrical and symmetrically spaced from the exterior surface of said cathode with respect to the axis of said cylindrical wall, said member beingl effectively extended into the space between said cathode and anode and havingv its interior wall in this portion shaped to form a conical channel coaxial with said cylindrical wall with its larger end toward said cathode and its smaller end terminating in a capillary opening, and means for starting a glowdischarge between said cold electrodes when the latter are at operating potentials the difference of which is below thestriking voltage comprising means for temporarily bringing said member to a potential not substantially greater than that of said anode.

5. A positive column glow discharge lamp comprising a vessel containing gas and enclosing electrodes in the form of a cold cylindrical cathode and a cold plate-like anode, the latterhav ing a small opening therein in line with the axis ofsaid cathode, and a hollow metallic member in part surrounding said cathode, the interior wall of said part being cylindrical and spaced a unifom' distance from the cylindrical exterior surface of said cathode, said ollow metallic member being effectively extende into the space between said cathode and anode and having its interior wall in this portion shaped to form a conical channel concentric with said cathode and aperture with its small end near and aligned with said aperture in said anode and terminating in an opening of a diameter at least as great as the maximum dimension of said aperture'.

6. A positive column glow discharge lamp comprising a vessel containing gas and enclosing electrodes in the form of a cold cathode and a cold anode and a metallic element forming a conical shaped channel between said electr'odes with its larger end toward said cathode, said cathode having an opening symmetrically positioned with respect to said channel, the walls of said cathode surrounding said opening and nearest said channel being circular in shape in a plane perpendicular to the axis of said channel, the diameter of said opening in said plane being not greatly diierent than the diameter of the large end of the channel.'

7. The combination as set forth in claim 6 in which said cathode is in the form of a hollow cylinder open at both ends and having its axis coincide with that of said channel.

O'ITO C. BLEICHER. 

